1. Field of the Invention
The invention relates to a triaxial cell for the testing of geomaterials, such as in particular rocks, grounds, is in the form of specimens especially cylindrical in shape.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
These cylindrically-shaped specimens may be subjected to different pressure, loading, temperature and draining conditions. In order to control these different parameters, the cell may be instrumented with pressure, temperature, internal or external displacement sensors as well as strain gauges. The pressure stresses may be axial, generated under the action of a hydraulic piston and radial on the side face of the specimen under the action of a pressurised fluid.
To that end, documents U.S. Pat. No. 3,975,950 or JP 5,871,432 divulge a triaxial testing cell essay which requires placement in a testing machine acting as a press, generally installed fixedly in laboratories.
To make such a cell autonomous, one may refer to the publication by BROWN S. F. AUSTIN G. AND OVERY, R. F. <<an instrument triaxial cell for cyclic loading of clays>> (GEOTECHNICAL TESTING JOURNAL GJJODJ VOL 3 No 4, December 1980, pages 145 to 152) or still document FR 2,663,123 which divulge a cell with a removable module placed on top of the cell and fitted with its own hydraulic piston capable of generating the axial stress necessary to the test. This autonomous cell thus enables onsite specimen testing, thereby avoiding any transport of specimens for the sampling site of to the to the laboratory.
The aforementioned cells, regardless whether installed fixedly or autonomous present a body comprising a cavity inside which the specimen is placed. The cavity provides between the side wall of the body and that of the specimen a peripheral chamber connected to a pressurising and controlled draining circuit. A fluid may be fed in order to exert a stress on the side surface of the specimen.
In the body, the specimen is positioned between a lower platen of a mount and an upper platen which receives the thrust necessary to the axial stress of a piston. This piston is guided translationally inside a bore through the upper wall of the body which may be monoblock with the side wall of the body or still be in the form of a lid removably fastened, generally screwed to tension rods. In practice, in a cell closed by a lid, when preparing the testing phase, the specimen may be wrapped in a membrane hugging its side wall and being positioned so as to rest on the lower platen. The specimen is covered by the side wall of the body, wherein the lid and its piston then close the cell, especially screwed on. In such a cell, the specimen thus rests simply on the lower platen and is not interconnected with the upper platen. Similarly, the upper platen is not interconnected with the piston of the lid so that it is solely possible to work in compression on the specimen. It should be noted that the same problem is raised for a cell whose upper wall of the body is monoblock with its side wall. However, it may be necessary to stress the specimen axially under tensile force, the difficulty then lies in finding a means for interconnecting the specimen under tensile force when the upper and lower platens, as well as the piston, housed inside the body are no longer accessible. The aim of the present invention is to remedy the drawbacks aforementioned by offering a triaxial cell for the testing of geomaterials enabling to exert onto the specimen a tensile stress especially along the longitudinal axis of the specimen
Another aim of the invention is to provide such a cell with easier alignment of the specimen assembly process.
Other aims and advantages will appear in the following description, which is given only by way of example, and without being limited thereto.